This invention relates to the field of electromagnetic wave antenna apparatus of the large bandwidth, diverse polarization and phase dispersionless type.
The prospect of replacing a plurality of single purpose antennas for a modern military aircraft with a lesser number of antennas that are capable of wideband and multi-functional operation is of significant interest in the aircraft and electronic arts. For reasons which include space availability, maintenance simplification and improved aerodynamic characteristics, the prospect of aircraft and spacecraft antenna count limitation is now carefully considered in the planning of each new aircraft and space vehicle and in each modification of existing equipment. The broadband radiation capability of the presently disclosed antenna together with its desirable polarization and phase characteristics suggest the possibility of its service in such applications. The antenna of the present disclosure can also be arranged for use in other environments such as satellite communications--in both the orbital vehicle and the earthbound receptor functions. In the latter, earthbound satellite receptor use the antenna herein disclosed can be supplemented with a parabolic dish or other reflecting element arrangements.
The prior patent art includes a large number of antenna arrangements, however, the characteristics of these antennas do not include the desirable bandwidth, phase, and polarization characteristics--especially the combination of these characteristics found in the present invention antenna.
The difficulty encountered in simultaneously achieving a combination of no phase dispersion with desirable spatial pattern and bandwidth characteristics in a single antenna is demonstrated by the commonly accepted compromises which lead to use of the log periodic antenna and the cavity backed spiral antenna. Each of these antennas can be arranged to achieve bandwidths exceeding a decade while also providing respectable spatial patterns and relatively desirable radiation efficiency. Along with these desirable properties, however, these antennas are known to have undesirable voltage standing wave ratios, values in the range of 2 to 1 or greater and to also exhibit severe time or phase dispersion of a transmitted or received signal. Such antennas, if fed with a very short pulse of radio frequency energy, a pulse of less than several cycles duration, provide a radiated electromagnetic waveform which contains severe phase and time dispersion effects and thereby cause the radiated waveform to be stretched in time. The combination of non-dispersion and broad frequency band characteristics is particularly unusual in the present state of the antenna art. For use in the spread spectrum signal environment and other broadband applications therefore, an improved antenna such as disclosed herein, is needed--especially in the specialized field of antennas for military use.